Tsugunori Okumura

Anomalous Enhancement of In-Diffusion of Plasma-Induced Defects in GaN upon Ultraviolet-Light Irradiation

We have shown that UV-light irradiation during plasma process anomalously enhances in-diffusion of the defects deactivating the Si donor in n-GaN. The region where the donor was deactivated by the plasma-induced defects became several times deeper upon the superimposed UV-light irradiation than that in the sample just exposed to plasma emission. It was also found that external light with the below-band-gap energy did not affect the defect in-diffusion, and hence we can suggest that the electron–hole pair generation is essential for the enhancement of defect in-diffusion.

Characterization of argon fast atom beam source and its application to the fabrication of resonant tunneling diodes

In this paper, energy distribution spectra of residual ion of the saddle-field argon (Ar) FAR source, and neutralization coefficients were experimentally evaluated for various process parameters by using an analyzer of our own fabricating. Moreover, GaInP/GaAs triple barrier resonant tunneling diodes (TBRTDs) were processed by using the argon FAB etching under appropriate condition and clear NDRs were estimated with high yield.

Scanning internal-photoemission microscopy: new mapping technique to characterize electrical inhomogeneity of metal-semiconductor interface

A new mapping technique, termed scanning internal-photoemission microscopy, has been presented to characterize the electrical inhomogeneity of metal-semiconductor interfaces. To obtain images of a Schottky barrier height, we have used two laser beams in a 1 µm band for which Si and GaAs substrates are transparent, and thus the proposed technique has been capable of probing the metal-semiconductor interfaces directly. The capability of this microscopy has been demonstrated by visualizing the parallel contact with two different metals, the existence of mechanical damage, and an ultrathin layer buried beneath a thick metal.

Properties of metastable hydrogen-related defects in n-type GaAs studied by isothermal deep-level transient spectroscopy

Metastable hydrogen-related defects (M3/M4) in n-GaAs were studied in detail by using isothermal deep-level transient spectroscopy. In order to clarify the electric-field dependence of the electron-emission process, the double-correlation technique was applied to both M3 and M4 defects. It was clearly shown that with increasing electric field, the M4 level observed around 140 K split into two discrete components labeled M4(1) and M4(2). The result supports the recent finding that the M4 defect consists of two different configurations. On the other hand, the M3 defect gave a single peak in the double-correlation spectra around 230 K. The electric field dependence of the emission rates suggests that the M3 and M4(1) defects have a donor-like nature, while the M4(2) defect is acceptor-like. It was speculated that the metastable defect coupling with the M3 level is only M4(2) out of two components of the M4 defect.

GaAs Schottky diodes with ideality factor of unity fabricated by in situ photoelectrochemical process

Schottky contacts to n-GaAs have been fabricated by means of a photoelectrochemical process in which in situ anodic etching of the substrate surface was performed in the same electrolytic solution as for electroplating of metals (Ni, Au, Sn and Pb). Measurement of the cyclic voltammogram was helpful in determining the applied voltages for in situ etching as well as metal deposition, and thus in fabricating good Schottky contacts reproducibly. The ideality factor (n value) of the fabricated diodes was unity for the substrate with an electron density of 2×1016 cm-3. The values of Schottky barrier heights determined by means of the I-V and C-V methods were in close agreement, and the chemical trend was clearly observed.

Mapping evaluation of damage effect on electrical properties of GaAs Schottky contacts

Scanning internal-photoemission microscopy has been applied to the evaluation of the effect of damage on electrical properties of Schottky contacts on GaAs. The photoyield in the damaged regions increased for n-GaAs and decreased for p-GaAs, whether the damage was a mechanical one or an implantation-induced one. The advantage of this technique has been demonstrated by (a) visualization of the damage effect in a single Schottky contact and (b) detection of an implantation-induced damage at a dose as low as 4 × 1010 cm-2.

Observation of 1/fα Noise of GaInP/GaAs Triple Barrier Resonant Tunneling Diodes

GaInP/GaAs triple barrier resonant tunneling diodes (TBRTDs) were fabricated and temperature dependence of noise measurements were carried out. The 1/fα dependent shaped noise was observed between 100 k and 300 MHz only when TBRTDs were biased in negative differential resistance (NDR) region. The result showed very small biased voltage dependence within the NDR region. The exponential factor α decreased as temperature increased. The possibilities of 1/fα dependent shaped noise were discussed.

Dominant Deep Level in Annealed Low-Temperature GaAs Layers Grown by Molecular Beam Epitaxy

Deep levels in the annealed low temperature molecular beam epitaxial (LT-MBE) GaAs layer were characterized by using the capacitance-deep-level transient spectroscopy (DLTS) technique in combination with a unique sample structure. We have fabricated the samples by inserting the LT-GaAs layer between two n-type semiconductive layers grown at normal substrate temperatures, like a sandwich. DLTS measurements revealed that one electron trap dominates the annealed LT-MBE GaAs layer. This dominant electron trap was very similar to the so-called EL3 level. By changing growth parameters of LT-GaAs layers, we found that the trap concentration of this EL3-like level was strongly related to Si doping and excess arsenic.

Low-Temperature Fluorination of GaAs Surface by CF4 Plasma

The GaAs surface was fluorinated at low temperatures in CF4 plasma. The constitution and the composition of the formed films as functions of the substrate temperature and exposure time were analyzed by X-ray photoelectron spectroscopy. The fluoride films whose thickness increased with the substrate temperature consisted of gallium oxyfluoride and free As. We have also examined the influence of the surface treatment of GaAs substrates as well as the capping layer on the fluoride films. The sulfur treatment delayed the initiation of fluorination, and a-Si:H capping layer prevented free As from evaporating out.

Contactless characterization of surface and interface band-bending in Silicon-On-Insulator (SOI) structures

Abstract The Kelvin-probe method is capable of determining electrical properties of the near-surface region of the SOI material as well as the BOX–substrate interface without any device preparation process and completely in a nondestructive manner. It is shown that a simple sandwich-type electrode configuration can be used for the contactless characterization of the SOI layer, when the capacitance between the vibrating electrode and the SOI surface is much smaller than the buried-oxide (BOX) and depletion-layer series capacitances. With the use of ultraviolet (UV) light source for the surface-photovoltage (SPV) measurement, the surface band-bending of very thin SOI layers can be characterized, while infrared (IR)-illumination is capable of searching deeper region.